Physisians are seeing more and more active patiants with knee injuries in there offices, mostly accociated with acute and chronic instability. The Postlateral knee instability is quite rare but is oftenly mistaken for other injurys not even closely related to the same problems like the more common anterior cruciate ligament (ACL), which can cause severe damage to the ligament. ACL is not uncommon and can lead to chronic knee injury and then create `anteromedial or anterolateral rotational movement of the tibia around the intact posterior cruciate ligiment`.Rotational instabilities are easily found in the lateral compartment rather than the medial. They are usually tested by the commonly known pivot shift test. These conditions are easily diagnosed by two simple tests in a clinical exams. Some diagnostic tests are the the external rotational recurvatum test and the postlateral drawer test. The external rotational recurvatum test hold the feet rotate inward and check to see if the leg rotates outward. For the postlateral drawer test pull the the leg forward under the knee cap and press back on the knee and the leg should come out like in the anterior drawer test.